SEGMENTATION OF THE PROSTATE IN MR IMAGES BY ATLAS MATCHING

Prostate cancer treatment by radiation therapy requires an accurate localisation of the prostate. For the treatment planning, primarily computed tomography (CT) images are used, but increasingly magnetic resonance (MR) images are added, because of their soft-tissue contrast. In current practice at our hospital, a manual delineation of the prostate is made, based on the CT and MR scans, which is a labour-intensive task. We propose an automatic segmentation method, based on non-rigid registration of a set of prelabelled MR atlas images. The algorithm consists of three stages. Firstly, the target image is nonrigidly registered with each atlas image, using mutual information as the similarity measure. After that, the best registered atlas images are selected by comparing the mutual information values after registration. Finally, the segmentation is obtained by averaging the selected deformed segmentations and thresholding the result. The method is evaluated on 22 images by calculating the overlap of automatic and manual segmentations. This results in a median Dice similarity coefficient of 0.82